The hand may be open, but those with experience of the guerrillas say that if it were outstretched further the number of desertions would be even higher.

"Many guerrillas are tired but taking the decision to leave is hard," says a rebel who recently demobilised after 31 years in the Revolutionary Armed Forces of Colombia (Farc).

"They're afraid, they don't know about the demobilisation scheme, and so there needs to be more communication."

The communication required is enough to give any advertiser a headache.

Radio reach

The ministry of defence not only needs to reach the rebels in their remote areas, it also needs to reassure them, its battlefield enemies, of its trustworthiness.

This month the ministry is launching a new campaign that aims to entice members of the Farc, the smaller National Liberation Army (ELN) and splinter groups.

Farc rebels have been fighting the Colombian state since the 1960s

Paramilitaries who did not disarm during the recent peace process with the government are ineligible.

To reach the guerrillas, radio has proved the best means of communication. One rebel commander is said to have been so keen to keep his troops from hearing demobilisation adverts that he promised to buy MP3 players to replace their radio sets.

Other commanders have simply banned all stations except the Farc's own broadcasts. Nonetheless, according to one demobilised guerrilla, "that station is pure revolutionary music and propaganda, so the guys tune into other stations too, even if they risk punishment".

Advertisements will also run on television, despite limited access among guerrillas.

"People think it's a waste of money," says Mr Jaramillo. "But most importantly you reach the families of the guerrillas, who can watch TV and who can then get the message through."

Other communication methods include leaflet-drops after combat operations, although this has been scaled back given that many of the messages are simply caught in the jungle tree-cover.

When commanders are killed, local radio broadcasts are organised to encourage their men to take the chance to desert.

Credibility gap

The guerrillas may therefore receive information about the demobilisation scheme, but they are conditioned to disbelieve them.

"The commanders say that all the media is put at the service of the state by the oligarchy," says a demobilised rebel.

The Farc can't compensate for the demobilisations because they're losing so much experience

Sergio Jaramillo Deputy defence minister

"They say that fighters who desert are killed by the army immediately as soon as they demobilise."

The government's own advertising has previously widened this credibility gap, with its unrealistic portrayals of life in the Farc.

One advert included the testimony of a supposed guerrilla alleging she had been raped.

In the new campaign, the government has tried to remedy these failures.

The radio adverts are narrated directly by ex-guerrillas in the hope that they will sound not only realistic but even familiar to the guerrillas listening.

Off air, some demobilised fighters have even called their ex-"comrades" to tell them that the government scheme is indeed genuine. Even among these unique consumers, word of mouth reigns.

Despite these advances, questions have been raised about the end results of demobilisation.

Official figures estimate that, while about 50,000 guerrillas have been captured, killed or demobilised in the past five years, guerrillas numbers have only dropped by about 8,000.

Stopping recruitment

According to Jose Fernando Isaza, the rector of Bogota's Jorge Tadeo Lozano University, the explanation is that the Farc and the ELN have managed to replace almost 85% of those lost with new recruits from rural areas.

Some argue that army recruitment undermines rebel demobilisation

Mr Jaramillo says that it is the quality, as well as the quantity, of rebel that should be considered.

"It's not a revolving door: you can't replace a 38-year-old with a child. The Farc can't compensate for the demobilisations because they're losing so much experience."

However, Mr Isaza's critique goes further. Although the demobilisation campaigns are "innocuous enough", he argues their success is undermined by the effect of another government advertising campaign - for army recruitment.

"Such advertising exalting the armed forces in fact promotes weapons in general. Most people who enter the forces do so for the protection that weapons bring, and they don't mind whether they join the guerrillas, the paramilitaries or the army."

The government rejects this link, but both it and Mr Isaza agree that the same close attention currently being paid to helping guerrillas demobilise should now be given to helping prevent their recruitment in the first place.

That may involve not just an advertising strategy, but increased security and job opportunities for those vulnerable to being recruited.

NUMBER OF DEMOBILISATIONS

Year

FARC

ELN

Paramilitaries

Other

Total

2003

1376

405

692

65

2538

2004

1300

333

1269

70

2972

2005

1135

301

1069

32

2564

2006

1558

359

470

73

2460

2007

2480

423

155

136

3192

Source: Colombian Ministry of Defence
Figures do not include those paramilitaries who disarmed collectively under an accord with the government.